In the southern part of the United States, it is common to plant a crop like wheat which is harvested in the early part of the summer and then to plant a second crop on the same ground after such wheat has been harvested. This can be done where the growing season is long enough. The farther north, the shorter the growing season. So there has been developed an east-west line across the United States to define a general boundary south of which such double cropping can be done, and north of which the growing season is too short for double cropping of the same ground. Obviously, the same problems exist in other parts of the world.
Normally, wheat is harvested using a combine which cuts the plant off, removes the kernels of wheat and then discharges the chaff out of the back of the combine onto the ground. Sometimes, if the wheat field was not planted all at one time, or germinates at different times, for example because of varying moisture conditions, it would not be cured uniformly across the field at harvest time. So instead of using the combine only, the wheat is first cut and windrowed. For example, by a machine of the type shown in FIG. 13 of U.S. Pat. No. 4,166,351, wherein a first crop such as wheat is cut and then delivered by conveyor belts to a central rearwardly extending conveyor belt which would windrow the wheat plants onto the ground for curing. Then after these wheat plants are cured, the wheat would all be of substantially the same moisture content and the windrow would be picked up and processed by a combine, thereby separating the wheat from the chaff, of course leaving the chaff or tailings on the ground.
If it is then later desired to plant the ground to a second crop, then usually a no-till planter would be used later to plant the second crop. Sometimes the chaff or straw would be removed first so it does not interfere with the planting of the second crop, and sometimes it would not be removed. In any event, it was heretofore necessary to use a combine to separate the grain from the rest of the plant before the second crop is planted, otherwise the first crop would be destroyed in the process of planting the second one.
Another problem with double cropping is that the discarged portions of the plant, such as the wheat straw, interfere with the planting of the second crop and therefore it is often necessary to remove the straw before planting the second crop.